One concern when users FTP into your server, is that by default users who have accounts can roam your server to view contents of files. VSFTPD by default does not allow user logins, it allows anonymous by default. Anonymous users by default are locked into the directory that they login to. This is exactly what you would want. However, if you set up user FTP accounts you will probably want to limit those users so they can only access their own files and not other users. In order to achieve this you must place them in a chroot jail.